Water-based adhesives are known in the prior art as labeling adhesives. Conventionally, such adhesives are applied to one side of a paper or plastics label, and this label is then bonded to a receptacle in a high-speed labeling process. For ease of processing, the receptacles, usually bottles, are already filled with contents when the label is affixed. Since the contents are refrigerated in many cases, the receptacles have an outer surface of which the temperature is below the ambient temperature, and this leads to condensed water forming on the outside of the receptacle. This condensed water is particularly problematic in the high-speed labeling processes that are used nowadays, since the labels do not adhere well to such wet surfaces and therefore easily slip out of position. A general aim is therefore to develop adhesives which also have good adhesive properties on wet surfaces.
A further requirement is that the labels can be easily removed without residue when the receptacles are recycled. For this purpose, it is desirable for the dried adhesive to be able to be dissolved quickly and easily in water or alkaline solutions.
In order to achieve good adhesion of a label to cold bottles wetted with condensed water, casein-based adhesives are predominantly used. However, as a natural product, casein is costly, not always available and is subject to significant fluctuations in quality. However, the advantageous properties of casein-based adhesives are currently still not completely reproduced by synthetic adhesives.
Suitable sealing adhesives play an important role in the field of packaging, cold-sealing adhesives being used to package temperature-sensitive goods, for example foods such as ice cream or chocolate. Heat-sealing adhesives are often used when producing blister packaging for pharmaceuticals. In the process, solvent-based systems are frequently used, since they have good sealing properties, bonding and resistance to many filling substances and environmental influences. However, this is disadvantageous in that working with substances containing high levels of solvent requires special protective measures. Therefore, production workers have to be protected against solvent vapors by appropriate measures, such as extraction systems, and complex explosion protection and fire protection have to be provided in the production department. There is therefore also demand for suitable water-based adhesives, which in particular have good sealing properties.
The problem addressed by the present invention is therefore to provide a synthetic adhesive which has the property of achieving good adhesion to cold and wet bottles and which therefore can replace the casein-based adhesives that are commonly used. Furthermore, the adhesive is intended to be able to be used as a sealing adhesive, in particular a cold-sealing adhesive.
Surprisingly, it has been demonstrated that this can be achieved by adhesive compositions which contain a combination of acrylate polymerizates with special polyvinyl-alcohol-based protective colloids. Commercially available polyvinyl alcohol is not suitable for use in the polymerization of acrylate dispersions due to its special chemical composition.